It's the ultimate example of "a fish out of water". Scientists have discovered that the mangrove killifish spends several months of the year living inside trees.

Mangrove killifish are able to physically change their bodies and metabolism

The remarkable creatures temporarily alter their biological makeup so they can breathe air, enabling them to survive out of water for long periods.

Biologists made the discovery when, while wading through swamps in Belize and Florida, they found hundreds of the odd fish hiding in the rotting branches and trunks of trees.

They learned that the fish had slithered to their new homes when the pools of water around the roots of mangrove trees dried up. Inside the logs, they were lined up end to end along tracks carved out by insects.

Dr Scott Taylor, of the Brevard County Environmentally Endangered Lands Programme in Florida, said the killifish were nestled together "like peas in a pod".

Mangrove killifish - Kryptolebias marmoratus - are also known to buck another biological norm. They are able to breed without a mate, making it the only known hermaphrodite vertebrate - animal with a backbone - that can self-fertilise.

Killifish can develop both female and male sexual organs, and fertilise their eggs while they are still in the body, laying tiny embryos into the water.

Around two inches long, the fish normally live in muddy pools and the flooded burrows of crabs in the mangrove swamps of Florida, Latin American and Caribbean.

They are able to physically change their bodies and metabolism to cope with life out of water. Their gills are altered to retain water and nutrients, while they excrete nitrogen waste through their skin.

But as soon as they return to water these changes are reversed.

They are not the only fish able to breathe air. The walking catfish of South-east Asia has gills that allow it to breathe in air and in water and the climbing perch of India can suffocate in water unless it can also gulp in air.

Wow very interesting by the way we also have walking cat fish here in Florida.unfortunetly The Everglades has become the home to Boa's from people getting rid of them after they become unwanted pets and they are creating havoc with the other wild life.